Fuel Gauge

NOTE: The fuel pump module may also be called the fuel tank unit.

NOTE: The remote fuel level sender may also be called the fuel level sensor.

On front wheel drive (FWD) vehicles, the instrument cluster receives the fuel level signal from the fuel level sensor, part of the fuel pump module. The fuel level sensor measures variable resistance in the fuel tank depending on the current fuel level. When the fuel level is low, the resistance in the unit is high (180 ohms ± 4 ohms). When the fuel level is high, the resistance in the unit is low (10 ohms ± 2 ohms).

On all wheel drive (AWD) vehicles, the fuel tank is a saddle tank design with 2 variable resistance senders, driven by floats, that provide resistances related to fuel height, in each side, to the cluster through hardwired inputs. The fuel level is read from each fuel sender through a 2-wire input. The fuel senders provide variable resistance between 180 ohms ± 4 ohms (empty tank) and 10 ohms ± 2 ohms (full tank). If the fuel level is low, the resistance in the fuel level sensor is high, causing the gauge to indicate empty (E). When the fuel level is high, the resistance in the fuel level sensor is low, and the gauge indicates full (F).

As fuel is consumed from the fuel pump module side of the fuel tank (the side with the fuel filler hose inlet), fuel is transferred from the secondary fuel level sender side of the tank (the side opposite the fuel filler hose inlet) to the fuel pump module side of the tank. The fuel pump module is connected to the secondary fuel level sender by a crossover line and transfers fuel when the fuel pump module is running.

The instrument cluster uses 4 different operating modes to calculate the fuel level:

Anti-slosh (default mode)
Key OFF fueling
Key ON fueling
Recovery

After a fuel fill up, the time for the fuel gauge to move from empty (E) to full (F) ranges from 2 seconds to 55 minutes depending on which operating mode the fuel gauge is in.

The default fuel gauge mode is the anti-slosh mode. To prevent fuel gauge changes from fuel slosh (gauge instability due to changes in fuel sender readings caused by fuel moving around in the tank), the fuel gauge takes approximately 55 minutes to go from empty (E) to full (F).

The key OFF fueling mode (2 seconds to read empty [E] to full [F]) requires 3 conditions be met:

The key must be in the OFF position during the entire refueling of the vehicle.
At least 15% of the vehicle's fuel capacity must be added to the fuel tank.
The instrument cluster must receive a valid key ON fuel sender reading within 1 second of the key being put into the RUN position. The key ON sample readings are considered valid if the fuel sender reading is between 10 ohms ± 2 ohms and 180 ohms ± 4 ohms.

If these conditions are not met, the fuel gauge stays in the anti-slosh mode, which results in a slow to read full (F) event.

The key ON fueling mode (approximately 90 seconds to read empty [E] to full [F]) requires 3 conditions be met:

The transaxle is in PARK (P) (automatic transaxle), or the parking brake is applied (manual transaxle).
The key is in the RUN position.
At least 15% of the vehicle's fuel capacity must be added to the fuel tank.

In key ON fueling mode, a 30-second timer activates after the transaxle is put into the PARK (P) position (automatic transaxle) or when the parking brake is applied (manual transaxle). When the 30 second time has elapsed and at least 15% of the vehicle's fuel capacity has been added, the fuel gauge response time is 90 seconds to read from empty (E) to full (F). When the transaxle is shifted out of PARK (P) or the parking brake is released, the fuel gauge strategy reverts to the anti-slosh mode. The key ON fueling mode prevents slow to read full events from happening if the customer refuels the vehicle with the key in the RUN position.

Recovery mode is incorporated into the instrument cluster strategy to recover from a missing fuel level input during a refueling event. Missing fuel level inputs result from intermittent opens in the fuel sender or its circuits. Recovery mode (empty [E] to full [F] approximately 20 minutes) is initiated when the following 2 conditions are met:

The instrument cluster is in the anti-slosh (default) mode.
The actual fuel level in the tank is greater than what is being displayed by the fuel gauge.